Aerobic life relies on oxygen for respiration and bioenergetic metabolism. Abnormality in the concentration of oxygen in human body is strongly implicated in the pathogenesis of a variety of diseases including cancer, myocardial infarction and stroke. Despite the importance of oxygen, accurate measurement and mapping of tissue oxygenation is difficult. Although many imaging modalities provide only relative or descriptive data on tissue oxygenation, the electron paramagnetic resonance (EPR) spectroscopy has the potential of providing quantitative data of oxygen in tissues, in vivo. In addition, the EPR technique has the unique capability of measuring absolute value of oxygen concentration with resolutions far better than any other technique. This is possible using molecular or crystalline paramagnetic probes whose EPR line-width is sensitive to molecular oxygen. This capability, when combined with the ability to obtain spatially resolved information using spectral-spatial (spectroscopic) EPR imaging, can provide accurate mapping of oxygen concentration. Despite significant advances in the development of highly oxygen-sensitive spin probes and low-frequency imaging instrumentation in the past decade, the use of this important technology for biological applications is severely limited by the prohibitively long acquisition times, usually tens of min. The main objective of this proposal is to develop novel image acquisition and reconstruction strategies to enable fast and high-resolution mapping of oxygen concentration in tissues. The proposal seeks to develop: (1) High-resolution 3D/4D spectroscopic imaging software and techniques for spatial mapping of oxygen concentration in tissues; (2) Fast 3D/4D spectroscopic imaging using spinning/sweeping magnetic field gradients; (3) Direct single-stage image reconstruction algorithm for progressive visualization of images from random-mode acquisitions; (4) Sensitive-mode adaptive data (SMAD) acquisition approach for increased data acquisition efficiency and image resolution; (5) Constant-time spectral-spatial imaging (CT-SSI) methods for fast and high-resolution imaging of oxygen. Preliminary studies show that up to 30-fold increase in the speed of image acquisition can be achieved compared to the conventional methods. The availability of these innovative procedures will enhance our ability to perform fast/high-resolution image acquisition. The technology should offer exciting new opportunities in the field of biomedical imaging of free radicals and oxygen.